diff --git a/java/src/org/broadinstitute/sting/gatk/walkers/annotator/PrimaryBaseSecondaryBaseSymmetry.java b/java/src/org/broadinstitute/sting/gatk/walkers/annotator/PrimaryBaseSecondaryBaseSymmetry.java
new file mode 100755
index 000000000..d6381332c
--- /dev/null
+++ b/java/src/org/broadinstitute/sting/gatk/walkers/annotator/PrimaryBaseSecondaryBaseSymmetry.java
@@ -0,0 +1,134 @@
+package org.broadinstitute.sting.gatk.walkers.annotator;
+
+import org.broadinstitute.sting.utils.Pair;
+import org.broadinstitute.sting.utils.ReadBackedPileup;
+import org.broadinstitute.sting.utils.BaseUtils;
+import org.broadinstitute.sting.utils.genotype.Genotype;
+import org.broadinstitute.sting.gatk.contexts.ReferenceContext;
+import org.apache.log4j.Logger;
+
+import java.util.List;
+
+/**
+ * Created by IntelliJ IDEA.
+ * User: chartl
+ * Date: Nov 21, 2009
+ * Time: 6:08:15 PM
+ * To change this template use File | Settings | File Templates.
+ */
+public class PrimaryBaseSecondaryBaseSymmetry implements VariantAnnotation{
+
+    private static boolean USE_ZERO_MAPQ_READS = true;
+    private static boolean USE_ZERO_QUALITY_READS = false;
+    private static String KEY_NAME = "1b2b_symmetry";
+    private static double epsilon = Math.pow(10.0,-12);
+    Logger logger = Logger.getLogger(PrimaryBaseSecondaryBaseSymmetry.class);
+
+    private boolean useConservativeVariance = true;
+
+    public void conservativeVarianceUsage( boolean b ) {
+        useConservativeVariance = b;
+    }
+
+    public boolean useZeroMappingQualityReads() { return USE_ZERO_MAPQ_READS; }
+
+    public boolean useZeroQualityReads() { return USE_ZERO_QUALITY_READS; }
+
+    public Pair<String,String> annotate(ReferenceContext ref, ReadBackedPileup pileup, List<Genotype> genotypes) {
+        Pair<Integer,Double> refSecondBasePair = getProportionOfReferenceSecondBasesThatSupportAlt(ref, pileup, genotypes);
+        Pair<Integer,Double> nonrefPrimaryBasePair = getProportionOfPrimaryNonrefBasesThatSupportAlt(ref, pileup, genotypes);
+        if ( refSecondBasePair == null || nonrefPrimaryBasePair ==  null ) {
+            return null;
+        } else {
+            logger.info("2b="+refSecondBasePair.second+" 1b="+nonrefPrimaryBasePair.second);
+            //double primary_secondary_stat = 1.0/Math.pow( transform(refSecondBasePair) - transform(nonrefPrimaryBasePair), 2);
+            double primary_secondary_stat = refSecondBasePair.second - nonrefPrimaryBasePair.second;
+            String annotation = String.format("%f", primary_secondary_stat);
+            logger.info("Second-base symmetry: annotating with "+annotation);
+            return new Pair<String,String>(KEY_NAME, annotation);
+        }
+    }
+
+    private double transform( double proportion, int depth ) {
+        proportion = proportion - epsilon;
+        if ( useConservativeVariance ) {
+            return proportion / ( Math.sqrt ( 0.5*(1-0.5) / Math.sqrt(depth) ) );
+        } else {
+            return proportion / ( Math.sqrt ( proportion*(1-proportion)/depth ) );
+        }
+    }
+
+    private double transform( Pair<Integer, Double> depth_prop ) {
+        return transform( depth_prop.getSecond(), depth_prop.getFirst() );
+    }
+
+    private Pair<Integer,Double> getProportionOfReferenceSecondBasesThatSupportAlt( ReferenceContext ref, ReadBackedPileup p, List<Genotype> genotypes) {
+        char snp;
+        try {
+            snp = getNonref(genotypes, ref.getBase());
+        } catch ( IllegalStateException e) {
+            logger.info("Caught: IllegalStateException -- "+e.getLocalizedMessage());
+            return null;
+        }
+
+        char[] secondaryPileup = p.getSecondaryBasePileup().toCharArray();
+        int depth = p.size();
+
+        int support = 0;
+        for ( char c : secondaryPileup ) {
+            if ( Character.toUpperCase(c) == Character.toUpperCase(snp) ) {
+                support ++;
+            }
+        }
+
+        double as_prop = ( ( double ) support ) / depth;
+
+        return new Pair<Integer,Double> ( depth, as_prop );
+    }
+
+    private Pair<Integer,Double> getProportionOfPrimaryNonrefBasesThatSupportAlt( ReferenceContext ref, ReadBackedPileup p, List<Genotype> genotypes ) {
+        char snp;
+        try {
+            snp = getNonref(genotypes, ref.getBase());
+        } catch ( IllegalStateException e ) {
+            return null;
+        }
+
+        int [] baseCounts = p.getBasePileupAsCounts();
+        int support = -1;
+        int depth = 0;
+        for ( char c : BaseUtils.BASES ) {
+            // ignore ref
+            if ( Character.toUpperCase(c) == Character.toUpperCase(ref.getBase()) ) {
+            } else {
+            // catch our snp
+                if ( Character.toUpperCase(c) == Character.toUpperCase(snp) ) {
+                    support = baseCounts[BaseUtils.simpleBaseToBaseIndex(c)];
+                    depth = depth + baseCounts[BaseUtils.simpleBaseToBaseIndex(c)];
+                } else {
+                    depth = depth + baseCounts[BaseUtils.simpleBaseToBaseIndex(c)];
+                }
+            }
+        }
+
+        if ( depth == 0 || support < 0 ) {
+            return null;
+        }
+
+        double as_prop = ( ( double ) support) / depth;
+
+        return new Pair<Integer,Double> ( depth, as_prop );
+    }
+
+    private char getNonref(List<Genotype> genotypes, char ref) {
+        //logger.info(genotypes.size());
+        for ( Genotype g : genotypes ) {
+            //logger.info("Genotype: "+g.getBases()+" Ref from genotype: "+g.getReference()+" Ref from method: "+ref);
+            if ( g.isVariant(ref) ) {
+                return g.toVariation(ref).getAlternativeBaseForSNP();
+            }
+        }
+        throw new IllegalStateException("List of genotypes did not contain a variant.");
+    }
+
+}